Elastic fluid turbine and method of operating the same



Feb. 7, 1933. o. D. H. BENTLEY ELASTIC FLUID TURBINE AND METHOD OF OPERATING THE SAME Filed May 5, 1928 Patented Feb. 7,

ua rso res OLIVER D. H. BENTLEY, OF NORFOLK, MASSACHUSETTS, A SSIGNOB TO B. F. STUR-TEVANT COMPANY, OF HYDE PAR-K, MASSACHUSETTS, A CORPORATION OF ISZLASSACHU'SET'J.S

ELASTIC FLUID TURBINEAND METHOD OF OPERATING THE SAME Application filed ma 5, 1928. Serial no. 275,416; 1 v

The present inventionrelates to elastic :tluid turbines and more particularly to elas out one or more nozzles for the more substantial changes in the load, smaller jvari-' ations being taken care of by a throttling of one or more of the nozzles. Such a method is reasonably satisfactory for a constant speed load, such as an electric generator, but is open to the disadvantage of a considerable loss in efiiciency when the load is such as to require operation of the turbine at different speeds. An example of the condition of variable speed operation may be found in the auxiliary turbines used in power plant oper ation for driving the mechanical draft fans. As the load on the station varies, the demand for draft likewise changes and the draft is ordinarily adjusted byrunning the fans at variable speeds. Inasmuch as the usual turbine employs identical nozzles which will operate most eificiently at only one speed, there is a decrease in efficiency and'awaste of energy when the turbine is called, upon to drive the fan at any other speed than that 40 each for a difierent speed and each con-' partlcular one for which the turbine nozzles are best adapted.

The object of the present invention is to devise an elastic fluid turbine which will opcrate with maximum efiiciency at any one of a number of different speeds.

With this object in view, the principal feature of the present invention comprises a turbine having a. plurality of individual nozzles,

structed and designed in such a manner as to introduce the fluid to the turbine with maximum efliciency at its own particular predetermined speed.

In order to secure such maximum efliciency the nozzle must bear a certain definite angular relation to the bucket walls of the rotor, and this angular relation will depend upon both the steam velocity at the nozzle and the bucket velocity past the nozzle. Thus, for

low speed operation, the difference in inclination between the low speed nozzles and the rotor buckets is small, while the nozzles which are to be supplied with greater amounts of steam but at the same velocity for higher rotational speeds have increasing inclinations from the rotor buckets, The desired angular relation is such that at the given steam velocity and rotor velocity the. steam will-enter thebucket'without abrupt change in its direction'of 'flow, The's ide walls of the bucket, therefore, at the steam receiving end are so inclined to the axis of the nozzle,'taking into consideration'the direction and velocity .of the steam and the movenient of the rotor, as to make such side walls in efiect parallel to the steam flow. Or expressed in another way, the angle of inclination between the bucket velocity and the relative steam velocityshould be the same as the angle of inclination of the bucket.

, Since the same buckets in the rotor are used for all the nozzles and obviously cannot be adjusted or changed to suit different conditions of steam velocity and rotor speed,the nozzles themselves must be so designed as to satisfy the required conditions.

The nozzles, which are formed with the usualreversing or re-dlrectlng buckets are preferably arranged'in sets, the separate nozzles of each set being identically constructed for operation with maximum efficiency at a single selected speed. When it is desired to run the turbine at a selected speed, one only of the nozzle sets is supplied withfiuid, the remainder being entirely out out of operation. In order to obtain speeds intermediate to the selected speeds, the turbine is supplied with fluid through nozzles of more than one from the rotor buckets. I I H set 10 is arranged for delivering a small quan tity of steam for low speed operation and is the different sets; andFig. 4 is a similar diagram showing the operation of the reversing buckets of a single nozzle. 7

The illustrated embodiment of the inven-' tion comprises a turbine, indicated generally at 4, to. which steamis supplied through the pipe 6,and which operates the variable speed fan 8. The turbine i isprovided with four .nozzle sets indicated generally at 10,12, 1e

and 16 being adapted respectively for "low speed, two intermediate speeds, and high 'sp eed operation. c

, Each nozzle set comprises four nozzle heads 20, each havin nozzle -22 and-a plurality of reversingbuckets23, 24 and 25. All of the nozzles areof the same expansion ratio, since they receive the steam atthe same pressure butfa re arranged atQdiiferent inclinations Each, nozzle of the placed at a slightinclination from the rotor buckets 26. See Fig. 2.' The nozzles of the 7 setl2lare somewhat larger, and are placedat a slightly greater inclination for higher speed 7 of rotation,.and the nozzles of thesets l i'and 16 are progressively larger and have[greater inclinations. The inclinations of the nozzles are diagrammatically indicatedbythe dotted lines a, b, 0, and d of Fig. 1. The sizes of the nozzlesof the several sets will depend uponthe amount of'working fluid which each set has to supply for satisfying the; load de-i mandsat tliexpartieular speed of operation of that set, All of the nozzles arelidentical as to expansion ratio (i. eQratio ofmoutharea to throat area) andthe nozzles of each particular set are of the same inclination and, preferably ofthe same size. g The control means for. connectingthe nozzles with the steam supply comprises an an.-'

nular distributingchamber .28 having a,plurali tyof inwardly extending valvelchamb ers 29, one for each nozzle, and connectedto the separate nozzles by suitable conduits. The

valve chambers are, dividedinto four, groups of four each, the groups be ngindicated at 30, 32, 34 and 36, for connecting respectively to the nozzles of the sets 10, 12, lt 16. Only one set of conduits, is shown in the rack and pinion connection158 is shown dia-.

grammatically in Fig. 1, being adapted for operation by the draft-demands on thestation. This automatic control is of any usual or preferred form and in fact may be at any one time, the remaining twelve valves being closed. The cam has a high part of sufiicient size to open four valves, the other valves being maintained closed by springs or other suitable means. When the demands on the plant are small, the four valves of the group will be open, thus running the turbine at its lowest speed from the nozzles of the set 10. As the. demand is increased the cam isrotated in the direction of the arrow, thereby successively cutting out nozzles of the set'lO and cutting in nozzles of the set 12. The particular positions of the valves shown in Fig. 1 are for operation on one of the nozzlesof the set 10 and three nozzles of the set 12. A further rotation of the cam' will open the valves of the group 32 exclusively. As the demands increase, the higher speed nozzle's will be cut in until the turbine finally operateson the four, nozzles of the high-speed set 16.7 The turbineoperatesat maximum efliciency at those selectedspeeds which call for operation from one set of nozzles alone, to the exclusion of all others, and at nearly maximum efiiciency at intermediate speeds when nozzlesof adjacent sets are employed.

' Thevector diagram of Fig. 3 illustrates the conditions for fullspeed and half speed operation,employing the nozzles of sets 16and.

12 respectively. In each case, the turbine is assumed to operate onthe nozzles of one set only, all pther nozzles being out of operation. I Theabsolute, peripheral speed of the'rotor isrepresented alonga horizontal line. For fullspeed rotation, this speed is represented bythe vector 0 6. At this time the nozzle set.

16 isopen while the remaining nozzles are cut: of]? from communlcation with thesteam sup ply; The'absolute' velocity of the steam is represented by the vector f6 which makes with the vector 0e an angle N, which angle isthe angle of inclination of the. nozzle axis with respect to thetangentto the rotor. The relative velocity ofthe steam with respect to the rotor is the difference of the vectors fe and 06 re resentedas the vector f0 making withthe orizontal an angle R. For most efficient operation, asalready explained, thisv angle should be equal to-the angle of inclination of the buckets with respect to the,

a gen Similarly, for half speed operation, the peripheral rotor speed is represented as the horizontal 1111609. The absolute steam velocity. is kg, which is of the same magnitude as thevector fe because the steam is admitted atthe same pressure and is-passed through ainozzle ofthe same expansion ratio. The angle of; inclination, however, is larger, more nearly approaching the value of the angle B,

and is represented as N The vector diflerence of by and g is ho, which is the relative velocity of the steam with respect to the rotor and which, owing to the proper design of the nozzle with the correct angle of inclination, also makes the same angle R with respect to the horizontal. Thus in each case, the inclination of the nozzle corresponds properly with the relative velocity of the steam with is 4.5", while the full speed nozzles have an inclination of 6. The inclination, as given above, is the angle between the nozzle and the bucket, represented in Fig. 3 as the angle efo for the high speed nozzles, and as the angle gho for the half speed nozzles. These angles are purposely exaggerated in the diagram.

Although the relative velocity is greater in the half speed case, it does not follow that the rotor speed will be greater, because in fact, the rotor speed is determined by the load and the steam supply imparted through the particular nozzle set employed. The nozzle set used at low speed is the set 10 which employs small nozzles for the purpose of limiting the amount of steam for driving the turbine. The vector diagrams of one-quarter and three-quarter speeds are not shown in Fig. 3, but may be constructed in an exactly similar manner. The nozzle inclinations in any case will be such that when the absolutevelocities of steam and rotor speed are compounded, the relative velocity will be along the line 0h.

The vector diagram illustrates the condition necessary for maximum efliciency, which condition is satisfied only whenthe turbine is run from the four nozzles of any onejset alone, all. other nozzles being cut out of operation. In other words, the turbine is then being operated at one of the selected speeds for which the particular nozzle set then in service is designed. At intermediate speeds, say. three-eighths speed, it is necessary to employ nozzles of both of the sets 10 and 12. The conditions for maximum efficiency are then not completely satisfied, because the inclination of the nozzles of set 10 is slightly too small and the inclination of the nozzles of set 12 is slightly too large to give exact velocity compounding of the absolute steam velocity with the rotor velocity. However, with provision for four selected speeds at full efliciency, the deviation from best conditions at any other speed is practically negligible.

In order to secure maximum efliciency of operation of the turbine, the reversing or redirecting bu'ckets of thenozzles must also be properly designed with respect to their inclinationsto the rotor buckets so that the steam will be discharged from suchreversing buckets into the rotor buckets without abrupt change in direction. Inasmuch as the velocity of thesteam in each reversing bucket becomes progressively lower in its passage throughthe several buckets of the nozzle unit, these buckets are given a progessively greater inclination totherotor buckets. The actual inclination of these reversing buckets to the rotor buckets will depend, just as does the inclination of the nozzle itself, both upon the steam velocity as it issues from thereversing bucket, and upon the speed of the rotor bucket.

In Fig. 2 is shown a nozzle set, such as the low speed set 10, comprising four nozzle units, each having the three reversing or re-directing buckets 23, 24 and 25'. Bucket 23, which is-next to the nozzle and receives the secondary steam as it is discharged from the rotor,

has a slightly less inclination tothe tangent than has the nozzle itself, because the secondary steamis at a lower velocity than the primary or nozzle steam. 1

Similarly the second or intermediate bucket 24 which receives the tertiary steam is. still less inclined to the tangent than bucket 23, and bucket25 which receives the quartenary steam is even less inclined than bucket 24. .For the purpose of illustration,

the inclinations are, shown in exaggerated In Fig. 4 of the drawing is shown a vector diagram illustrating this varying inclination of the reversing buckets of a nozzle unit. In this diagram the horizontal vector jlc represents the rotor speed, the vector 7d represents the absolute steam velocity from the nozzle,and the vector Zj represents the relative steam velocity with respect to the rotor.

The angle P represents theinclination of the rotor bucketfrom the tangent and the angle Zkj shows the inclination of the nozzle to the tangent of the rotor.

- Since the rotor velocity is the same for all the buckets of the nozzle unit, the vector jlc will be'the same for the several reversing buckets. :Theangle P of the bucket, of course,remains constant. The several vec tors mic, nk, and sic represent the absolute steam velocities of discharge from each of the reversing buckets 23, 24 and 25, and the "angleotinclination of each of these buckets is IOS.

represented by the angles mkj, nkj, and sky respectively. V

lVhile in the accompanvlng specification and drawing there is described and shown a construction in whlch the steam is supplied to all the nozzles at the same pressure and,

therefore, the nozzles all have the same expansion ratio, the present invention is not limited thereto except where so specifically set forth in the claims, but may be embodied in a construction in which the steam is supplied to the different nozzles at different pressures. Such a construction is shown and described and claimed in my companion application of even date herewith.

The present invention contemplates in its broader features the use of a plurality of nozzles or sets of-nozzles, each capable of independent use', and each designed to drive the rotor at a particular speed, the inclination of the nozzles being such that each nozzle or set otnozzles operates to drive the rotor at its own particular speed with maximum efficiency. The invention further contemplates the provision with each nozzle of one or more reversing or re-directing buckets each so inclined as to return the steam to the buckets of the rotor with maximum efli ciency. v

Another feature of the present invention is the operation of the turbine at speeds intermediate to the selected speeds by employment of nozzles of more than one set at a time.

. "Moreover, it is not necessary, although preferable, that the nozzles of each set shall be of identical inclination. It is within the.

purview'of the'present invention to employ nozzles, all of different and progressively varying inclination. VVith'this construction, when a plurality of nozzles are supplied at one time, there will be no selected speedsat which theconditions for utmost efficiency are completely satisfied, but the deviations from best condition will be small at all speeds. v

. Although the invention has been described inconnection with nozzle sets each having a plurality of nozzles, and although such construction is desirable from the standpoint of nicety of control, the invention is'not-limited to this particular arrangement, and the term n0zzle set as used in the claims, except where it is specifically limited to a plurality of nozzles, is inclusive of a single nozzle. Having thus described the invention, what is claimed is:

1. A variable speed elastic-fiuid turbine having, in combination, a rotor provided with buckets, a plurality of nozzle units constructed and arranged'for operation of the rotor at different speeds, each nozzle unit comprising'a nozzle and-a plurality of reversing' buckets, the inclination of each bucket along the path of flow of the fluid through a nozzle unitbeing, progressively less with respect to a rotor tangent, andmeans for supplying workingfiuid to one of the nozzle units to operate at a selected speed.

2. A variablespeed elastic fluid turbine having, in combination,- a rotor provided' With buckets, a plurality of nozzle units constrncted and; a-rrange'd' for operation of the rotor at different speeds, each nozzle unit comprising a nozzle and a plurality of revers ing buckets, the inclination of the nozzles with respect to a rotor tangent being pr'ogressively less with thenozzles for operating at the progressively higher speeds, and the reversing b-ucketof each unit along the path of flow of the fluid having a progressively less inclination with respect to such tangent,

andmeans for supplying a working fluid to one of the nozzle units to operate at a selected speed, r

3.- A -variable' speed elastic fluid turbine having, in combination, a rotor provided with buckets, a plurality of nozzles of pro gressively varying' incl inations with respect to the buckets, and progressive'control means having provision foroperating the turbine from a predetermined number of nozzles, and means for operating the control means the same n'umber'of nozzles, a valve for each nozzle, and progressive control means for maintaining" a predetermined number of valves open, said means having provision for progressively cutting in nozzles of larger in clinations' and cutting out nozzles of smaller inclinations to increase the speed.

In testimony whereof I have signed my name to this'specification.

OLIVER D. H. BENTLEY. 

